Printing machine and printing blanket therefor



July 24, 1962 E. GURIN 3,045,595

PRINTING MACHINE AND PRINTING BLANKET THEREFOR Filed April 7, 1960 i ammmmfim V up 0' INVENTOR Z'mrzzzeZ 624777;,

ATTORNEY 3,045,595 PRINTING MACHINE AND PRINTING BLANKET THEREFOREmanuel Gurin, P.0. Box 10142, Caparra Heights, San Juan, Puerto RicoFiled Apr. 7, 1960, Ser. No. 20,629 2 Claims. (Cl. 101415.1)

The present invention relates to printing machines, and especiallyprinting machines of the offset type. More particularly, the presentinvention relates to a printing cylinder for such machines and incombination therewith a novel printing blanket formed of elastomercoated dimensionally stable smoother paper.

In offset printing, the ink for printing comes from the impressionreceiving contact on to an impression receiving and yielding printingblanket surface and then into contact with the surface to be printed soas to make an imprint thereon.

Printing cylinders of offset printing machines are ordinarily providedwith a printers blanket composed of a plurality of layers of fabricconventionally bonded and surface-coated with a composition layer havingas a major constituent natural rubber, synthetic resins, and syntheticrubber.

Heretofore, it has been accepted that these offset printing blankets hadto be composed of a plurality of layers so as to insure the properstrength and thickness to the blanket. The multi-ply printing blanketscurrently used are difficult and expensive to manufacture and have to bediscarded in toto upon surface wear, and for other reasons such assurface damage, etc.

These difficulties and expense have been obviated in accordance with theinvention disclosed in my copending application, Serial No. 603,600,filed August 13, 1956, now U.S. Patent No. 3,012,498, wherein a novelsingle ply printers blanket for an offset printing press cylinder wasformed of high tenacity cellulose acetate woven smooth rayon material,said single ply having a thickness of about .005 to 015 inch and astrength of between 150 and 500 pounds per lineal inch With an inkreceiving rubber or synthetic elastomer coating on said single ply of athickness of from .015 to .025 inch, said single ply being superimposedover a packing blanket which covers said offset printing press cylinder,the total thickness of said single ply and packing blanket being that ofa conventional multi-ply blanket. With lesser amounts of ink receivingcoating, the normal wear of the blanket caused the underlying weave tostrike through at which point an impression of the weave was picked upin offset printing use and the blanket had to be discarded in toto.

The freedom from surface irregularity, which is found I by use of asmooth surfaced dimensionally stable paper and which is difficult toachieve with a woven backing eliminates this disadvantage at asubstantial saving in cost of materials. The inherent irregularity inthe fabric blanket of my copending application Serial No. 603,600, filedAugust 13, 1956, may be partially smoothed out by stretching andtightening the fabric blanket on the cylinder. These irregularities arenot present in the dimensionally stable smooth surfaced paper backedblanket of the invention. In the light of the excellent printingachieved by the present construction without the requirement forexcessive stretching of the blanket substantial ice advantages are foundover the embodiment of my copending application. A minute movement ofthe stretched woven base due to tension is avoided in fitting theblanket to the cylinder and improved features of the printing surfaceresults.

Heretofore there have been used hard paper covered tympan rollers toprotect the paper which is printed by a printing cylinder; examples ofsuch paper covered tympan rollers being shown in Page, U.S. Patent No.2,544,- 279 and Woodell, U.S. Patent No. 2,232,989. These hard papercovered tympan rollers are obviously different in their use in printing,since they serve as a backing for the reverse side of the paper which isprinted by the printing cylinder whereas the offset printers blanketconstruction of elastomer coated thin paper of the present invention perse constitutes the printing surface in offset printing.

There has also been used heretofore soft press blankets in high speednewspaper printing, a soft paper or felt covered press blanket tocushion the cylinders which are opposed to the impression cylinder,these termed press blankets and also serving to protect the reverse sideof the paper being printed. Examples of these heavy paper or felt pressblankets are shown in Fennone, U.S. Patent No. 1,891,150 and Schacht,U.S. Patent No. 1,897,864. These thick felt structures also do notfunction as an ink transferring structure as does the elastomer coateddimensionally stable paper printers blanket of the present invention.

In the press blankets and tympan blankets of these cited prior artstructures, the common requirement which is to be met is to prevent thereverse side of the paper being printed from becoming deformed,indented, or cut by the action of the hard metal type surface andprinting is not by the blanket covering but by the type face itself.

In offset printing, the expectation heretofore has been that a strong,thick multi-ply laminated structure was essential in order to providestrength and an adhesively secured built-up structure which is necessaryas the dimensionally stable backing for the clearance between the offsetroller and the paper sheet feeding roller operating at high speed. Themulti-ply laminate was also deemed essential in providing an unyieldingsmoothness of the printing surface. The dimensional stability of theoffset roller blanket was achieved by a single composite blanketstructure. It was particularly unexpected that the laminated printingblankets heretofore employed for offset printing could be eliminated infavor of a single ply of elastomer coated smooth and dimensionallystable paper which is backed by a separate non-adhered backing member toabsorb shock during printing will achieve highly eificient continuousoffset printing, and to attain long wear of the blanket with surprisingfreedom from registration difficulties even after it has been subjectedto long printing usage.

It has been discovered that the single backing layer'consisting ofsmooth dimensionally stable paper coated with elastomer when backed withanother independent shockabsorbing backing sheet, which preferably mayalso be smooth surfaced multiple ply paper, or paper board of subtractedthickness provides superior smoothness and dimensional stability forprinting blanket, the smoothness and stability being superior to thatwhich results when an adhesive is interposed between the elastomercoated paper and a separate backing sheet and also being better thanthat which utilizes a soft separate packing material in directsupporting relation to the single ply coated paper blanket.

It has been further observed that the use of the single ply coatedblanket of the invention with a paper backing having a hard surface,separate and non-adherent paper surface permits much sharper impressionduring offset imprinting depending upon the surface hardness of thestock being printed. This sharper impression is aided by using eventhinner coatings of elastomer for the offset blanket. For example, arubber coating on the high tensile strength paper backing which is asthin as .003 to .005 inch provides very sharp impressions for offsetprinting on hard metal surfaces such as metal can bodies. In instanceswhere a relatively rough and imperfect softer surface is to be printed asomewhat thicker coated layer would be employed.

It is not only the dimensionally stable and smoothness characteristicsof the good strength paper base which afford superior printingcharacteristics since the paper backing must also be sufficientlyflexible to overcome wrinkling of the blanket. The flexibility must notbe had at a surface of sufficient smoothness to provide uniformity inprinting. In the laminated printers blankets, a multiply paper backingwould tend to make the blanket too stiff and unyielding, wrinklesdeveloping before mounting the blanket or appearing during usage due toimproper mounting could not be easily smoothed and this would result indiscarding the blanket when this condition occurred. Similarly the useof thin hard metal backings although capable of providing excellentsmoothness, suffers the same defect as the multi-ply laminated blankets,e.g., wrinkles cannot be ironed out by tensioning during mounting of theblanket on the offset roller.

It is one of the objects of the present invention, therefore, to providefor an offset printing press having a printing cylinder, novel blanketmeans including a single ply covering blanket of high tensile strengthpaper and completely independent of a packing blanket, which ispreferably a dense hard packing for placing the printing blanket inproper relation to the rollers used for bringing the paper into contacttherewith.

Another object of the invention is to provide a novel high tensilestrength single ply printers blanket for offset printing formed offlexible smooth surfaced, dimensionally stable, paper having a thicknessof between about .003 to about .025 inch and coated with an inkimpression receiving elastomeric coating varying in thickness from about.003 to about .025 inch, said blanket being adapted for use with anindependent shock absorbing inner packing blanket and holding said innerblanket in place on an offset printing cylinder.

Another object of the present invention is to provide in combinationwith a printing cylinder a plurality of elastomer coated single plypaper printing blankets and an inner packing blanket, the outer singleply paper printing blanket covering and holding the inner blankets inplace on a printing cylinder of an offset press.

Other objects and advantages of the present invention will becomeapparent from the subsequent description and figures of the drawingwherein:

FIG. 1 is a diagrammatic section of a portion of the blankets, and

FIG. 2 is a diagrammatic end elevation of a printing cylinder havingmounted thereon a pair of blankets of varied lengths.

Referring to the figures of the drawing, FIG. 1 representsdiagrammatically an independent top or covering blanket indicated ingeneral at 10, comprising a high tensile strength paper 11 and anink-receiving coating 12. At 13 there is indicated diagrammatically alower or packing blanket which is preferably of a single ply as shown.

Referring to FIGURE 2, there is shown at 14 a conventional printingcylinder of an offset printing press. As shown, the printing cylinderhas mounted thereon the covering blanket 10 and the packing blanket 13.As indicated at 15, the packing blanket 1-3 is of a lesser length thanthe covering blanket 10. The ends 16 and 17 of the blankets 10 and 13,respectively, are held between a bar 18 and a holding bar 19, and meansare provided to hold the bars together and to the cylinder as indicatedby the screw or bolt 20. Rotatable with the cylinder is a conventionaltightening roll 21 having a ratchet wheel 22 rotatable therewith. Theend 23 of the blanket 10 is wound about the tightening roll and the rollis held in position by the pawl 24 cooperating with the ratchet wheel22. By this means different stretch of the two blankets 10 and 13 isavoided.

The backing layer 11 of the offset blanket 10 is formed of a singlesheet of high tensile strength paper of uniform thickness of about .003to about .025 inch, preferably high tensile strength kraft paper,calendercd or supercalendered to a hard surface finish and having aMullen bursting strength of between 50-200 pounds for a base weight of20 to pounds a tensile strength of between 20 and pounds between 20 and90 pounds base weight. The high bursting kraft paper is preferredbecause it is readily available commercially in the uniform thicknessbetween .008.025 inch and in this form possess superior qualities forthe blanket of the present invention. These properties of kraft paperare shared by other strong fiber papers made as smooth dimensionallystable sheets such as paper made from jute fibers, from sisal fibers,from hemp fibers and from long wood pulp fibers by the sulfite process.It will be understood that these papers are like the kraft paper of theabove description and exhibit approximately equal tensile or tearingstrength in both the long and cross directions so that when sharplycreased the wrinkles which form may be smoothed by tensioning the paper.The paper should be dimensionally stable i.e., substantially incapableof stretch or distortion under the tension which is necessary formounting the blanket.

The ink receiving layer 12 has a uniform thickness of from about .003inch to about .025 inch preferably in the range of .003-.008 inch whenprinting is to be done on hard surfaces such as metal and preferablybetween .015- .022 inch when printing is to be done on soft surfacessuch as cardboard.

Elastomer film thickness between .005 and .020 inch are suitable forofiset printing of letter writing stock, the heavier thicknessesproviding longer blanket life.

The synthetic elastomer material is composed of natural or syntheticrubber of the types known in the art. These are, for example,polymerized butadiene, acrylonitrile copolymers, olefin polysulfides,polymerized chloroprene, etc. The rubber may compose 50% or more of thefinished composition and may contain the usual acceleratorsantioxidants, reinforcing pigments, fillers, softeners, plasticizers,activators, and of course a vulcanizing agent such as sulfur. The totalthickness, therefore, of the covering blanket will be between .020 and.040 inch and preferably approximately .030.

As antioxidants there may be utilized such materials as Neozone A(Dupont), i.e., phenyl-alpha-napthalamine, as well as others well knownin the rubber compounding art. As softeners there may be such materialsas tricresyl phosphate, paraffin, dibutyl phthalate, etc. Asaccelerators there may be used such materials as Santocure (Monsanto) orN-cyclohexyl-Z-benzothiazyl-sufonamide, mercaptobenzothiazol,tetramethylthiuramdisulfide, etc.

The reinforcing pigments or fillers may include any of the variousgrades of carbon black, whiting, clays or the like. The compositionshould also preferably contain zinc oxide as an activator for theaccelerator and stearic acid as plasticizer and aid in vulcanizing.Preferably in order to render the composition spreadable, there isincorporated with the solid materials a suitable solvent, preferably ahydrocarbon such as toluol, in the proportion of one part of the solidingredients to one part of toluol or in somewhat greater proportions.

Since the conventional printers blanket in the case of a three-plyblanket has a thickness of from .062 to .066 inch, and from .072 to .076in the case of a four-ply blanket, the packing blanket 13 shouldpreferably be of a thickness so that the composite dimension of both thecovering blanket .10 and the blanket 13 is equal to these figures.

It is preferred that the packing blanket 13 consists of a hard basematerial and the utilization of one or more of the high tensile strengthpaper printing blankets of the present invention to make up thenecessary thickness represents a novel, advantageous and convenientassembly which has not been heretofore employed.

As mentioned above the provision of a hard independcut and separatebacking surface improves the printing characteristics of the presentblanket, this hard surface providing a relatively unyielding backingagainst which the outer blanket is tensioned and unwrinkled andimparting dimensional stability which cannot be achieved if a softpacking material is employed.

As may be understood, depending on the particular undercut of theprinting cylinder, there may also be used with the blanket and theunderlying paper blanket the conventional paper underpacking andmake-ready.

The following specific example serves to illustrate a suitable coveringblanket 10:

Example High tensile strength kraft paper having a hard surface finishand having a Mullen bursting strength of 90 pounds tensile strengthbetween 38 and 70 pounds in a thickness R of .010 inch is conventionallycoated with a composition of the following constitution:

Bnna N, 100 parts by weight; Santocure 1, one part by weight; Neoxone A,one part by Weight; carbon black, 50 parts by weight; dibutyl phthalate,ten parts by weight; zinc oxide, five parts by weight; sulfur, two partsby weight; and stearic acid, one part by weight. To the foregoing solidconstituents for each part of solid there was added one part of toluol.Thte mixture was suitably milled and then coated on the fabric in aconventional manner to form a smooth coating of .020 inch in thickness.It was then vulcanized at 290 F. for approximately two hours. Theresultant single ply printers blanket was mounted upon a cylinder of anoifset printing press in the manner indicated in FIGURE 2 over a packingblanket and was capable of receiving sufiicient tension to maintain boththe cover blanket and the packing blanket on the printing cylinder.

The characteristics of other suitable kraft paper which is similarlycoated is shown below:

1. In an offset printing press having an offset cylinder for receivingan inked impression, blanket means for covering said cylinder includinga packing blanket, an independent covering blanket consisting of asingle ply of dimensionally stable flexible, hard surfaced paper havinga thickness of .003 to .025 inch whereby the covering blanket has arelatively smooth surface and a Mullen bursting strength of between 50and 200 pounds, and an ink-receiving coating consisting of vulcanizedelastomer on said single ply of from .003 to .025 inch, the totalthickness of said blanket means being that of a conventional mnlti-plyblanket and means to retain said blankets on said offset cylinder.

2. In an offset printing press having an offset cylinder for receivingan inked impression, blanket means for covering said cylinder includinga packing blanket, an independent covering blanket consisting of asingle ply of dimensionally stable, hard surfaced paper having athickness of .003 to .025 inch whereby the covering blanket has arelatively smooth surface and a Mullen bursting strength of between 50and 200 pounds, and an ink-receiving coating consisting of vulcanizedelastomer on said single ply of from .003 to .025 inch, the totalthickness of said blanket means being that of a conventional multiplyblanket means for securing one end of both blankets to said cylinder andmeans to secure the other end of said covering blanket to said cylinderwhereby said covering blanket retains said packing blanket on saidcylinder.

References Cited in the file of this patent UNITED STATES PATENTS364,287 Pfeil June 7, 1887 1,211,706 Hoerbelt Jan. 9, 1917 1,892,623McElroy Dec. 27, 1932. 2,020,479 Sites Nov. 12, 1935 2,027,322 Rice Jan.7, 1936 2,793,588 Stempel May 28, 1957

